Arrangement for multi-stage heat pump assembly

ABSTRACT

A gasdynamic arrangement for a multi-stage centrifugal turbomachine, such as a two-stage compressor, comprising two coaxial impellers assembled on a common shaft with axial intake ports and radial peripheral discharge zones, the intake ports of the two impellers preferably pointing away from each other; a cylindrical vessel concentrically housing the impellers and the intake duct; a partition wall between the two impellers having a first and a second group of apertures; a first array of curved ducts conveying the flow from the first impeller discharge zone to the first group of apertures in the partition wall, the flow further passing through a chamber in the vessel to the intake port of the second impeller, and a second array of curved ducts conveying the flow from the second impeller discharge zone to the second group of apertures in the partition wall, the flow further going to the discharge port, the two flows bypassing each other in opposing directions at the partition wall.

This application is the national phase under 35 U.S.C. Å 371 of PCTInternational Application No. PCT/IL01/00186 which has an Internationalfiling date of Feb. 28, 2001, which designated the United States ofAmerica.

FIELD OF THE INVENTION

This invention relates generally to gasdynamic schemes in turbomachinessuch as centrifugal compressors used in heat pumps, and moreparticularly to compact gasdynamic arrangements for high-capacitymultistage centrifugal compressors working with water vapor.

STATUS OF PRIOR ART

Various industrial applications, e.g. desalination, water chilling, andice-making, require massive production of cold, i.e. cooling largequantities of air, water or other coolant. A known method of absorbingheat, when water is used as coolant, is boiling the coolant water underreduced pressure at the respective low temperature. In order to disposeof the heat contained in the evaporated water, the vapor must be broughtto higher temperature and pressure by suitable thermodynamic process andfinally be condensed transferring the heat to an available heat sinksuch as water from a cooling tower. The temperature difference betweenthe compressed vapor and the heat sink, plus some additional temperaturedrop needed to drive the dynamic heat transfer, all expressed in unitsof the saturated water vapor at those temperatures, determine thecompression ratio (CR) of the compressor powering this process.

From the viewpoint of economics, it is desirable to employ thecompression process in a single-stage compressor. But when by reason ofvarious design considerations, a single-stage compressor is impractical,it is then the practice to use two or more compressor stages in series,as disclosed in the U.S. Pat. No. 5,520,008 to Ophir et al. Implementingintercooling of the gas/vapor between stages raises the thermodynamicefficiency of the operation and lowers the consumption of mechanicalpower.

In the heat pump assembly described in the Ophir et al. patent, use ismade of a pair of individual centrifugal compressor units, each havingits own impeller shaft and a bearing house therefor, as well as its ownmotor to drive the shaft. In this arrangement, the two motors are placedon opposite sides of the compressor chamber.

In a multi-stage centrifugal compressor in which the stages areassembled in series, the geometries of the vapor passages must becarefully designed so as to convey in an energy-efficient manner thepartially compressed vapors from the discharge zone of a preceding stageat the periphery of its impeller to the central intake port of thesucceeding stage. Often, intercooling of vapors between the stages isrequired in order to attain optimum thermodynamic efficiences. Theserequirements further complicate the geometry of the vapor passages, andalso enlarge the physical dimensions and cost of the heat pump assembly.This is especially true of high throughput heat pump units of largediameters.

Such machines as in U.S. Pat. No. 5,520,008 have been built and areoperating well, but a more compact solution is very desirable, in orderto reduce cost and facilitate installation and maintenance work inconfined spaces, such as service basements and galleries of largehotels, office buildings, shopping centers, etc.

A more compact arrangement is disclosed in DE 1803958A describing atwo-stage turbomachine (compressor) with intermediate heat exchangerswhere the impellers of the two stages are disposed coaxially opposite toeach other and constitute one body. The intake duct of the turbomachineis a cylinder or conical pipe coaxial with the impellers and is disposedat the side of the first stage. The discharge flow of the first stage isconveyed by a plurality of first discharge ducts to an annular heatexchanger coaxial with the impellers, embracing the intake duct anddisposed also at the side of the first stage. Then the flow makes asharp turn by 180° into a peripheral annular channel embracing the heatexchanger and is directed to the intake port of the second stage. Thedischarge flow of the second stage is conveyed by a plurality of seconddischarge ducts to another annular coaxial heat exchanger ending with adischarge port and disposed between the intake duct and the first heatexchanger, also at the side of the first stage. This arrangement placesfour coaxial flows and two heat exchanger volumes at one side of theimpeller group, which involves high hydraulic losses.

CH 102821 discloses a four-stage turbomachine (compressor) with twoparallel shafts driven by one motor by means of a gearbox. The first andthe second stage impellers are on one shaft, in opposition, while thethird and the fourth stage impellers are on a second shaft. The intakeduct is disposed laterally to the first shaft. The discharge duct of thefirst stage conveys the flow from the periphery of the first impeller tothe intake of the second stage along a path approximately following thesurface of a torus coaxial with the first shaft, while the dischargeflow of the second stage is gathered in a space defined by the sametorus and conveyed via one lateral pipe to the intake of the third stagecoaxial with the second shaft. This arrangement is asymmetric and doesnot accommodate heat exchangers or other elements in the flow pathbetween coaxial stages.

SUMMARY OF THE INVENTION

In view of the foregoing, the main object of the invention is to providenovel gasdynamic arrangements particularly suitable for buildingeconomically feasible, compact and efficient turbomachines such asmulti-stage, high-compression, high-throughput gas or vapor centrifugalcompressors for heat pumps, and a novel design of a heat pumpparticularly suitable for use with such compressors.

In accordance with a first aspect of the present invention there isprovided a gasdynamic arrangement for a multi-stage centrifugalturbomachine having an intake duct and a discharge port, comprising:

-   -   two impellers with axial intake ports and radial peripheral        discharge zones, the intake port of the first impeller being in        fluid communication with the intake duct, the two impellers        being located at two sides of an imaginary plane crossing their        common axis;    -   a first means for conducting the flow from the peripheral        discharge zone of the first impeller to the intake port of the        second impeller along a first flow path including a plurality of        first curved ducts in axysimmetric arrangement;    -   a second means for conducting the flow from the peripheral        discharge zone of the second impeller towards the discharge port        of the machine along a second flow path including a plurality of        second curved cuts in axysimmetric arrangement;    -   wherein the first and the second paths leave the respective        peripheral discharge zones bending gradually towards the        imaginary plane, cross the imaginary plane in opposite        directions and, after the crossing, the two flow paths lie        entirely at different sides of the imaginary plane.

In a particular embodiment of a two-stage compressor the gasdynamicarrangement comprises:

-   -   two coaxial impellers assembled on a common shaft, the intake        ports of the impellers preferably pointing away from each other;    -   a cylindrical vessel concentrically housing the impellers and        the intake duct;    -   a partition wall between the two impellers having a first and a        second group of apertures;    -   a first array of curved ducts conveying the flow from the first        impeller discharge zone to the first group of apertures in the        partition wall, the flow further passing through a chamber in        the vessel to the intake port of the second impeller, and a        second array of curved ducts conveying the flow from the second        impeller discharge zone to the second group of apertures in the        partition wall, the flow further going to the discharge port,        the two flows bypassing each other in opposing directions at the        partition wall.

In accordance with a second aspect of the present invention, there isprovided a gasdynamic arrangement comprising an annular condenserchamber disposed concentrically around an intake duct within a heat pumpassembly.

Both aspects are aimed at the development of more compact turbomachinedesigns. In the implementation of the arrangement of the first aspect ofthe present invention in a two-stage compressor, this is achieved by theusage of a short common shaft supported by a single bearing housesituated between the impellers (stages) and driven by a single motor. Inthe implementation of the arrangement of the second aspect of thepresent invention in a heat pump assembly, this is achieved by areduction of the assembly overall length. The employment of bothgasdynamic arrangements provides for a highly integrated heat pumpassembly, wherein all functional components of the system with thepossible exception of the driving motor—multiple compressor stages,evaporator, condenser, intercooling and mist-elimination equipment—areincorporated within a single cylindrical vessel without external ducts.The assembly is characterized by reduced gas/vapor pressure losses,thereby improving the compression ratio and enhancing heat pump economy.The cost of manufacturing this integrated heat pump assembly isconsiderably lower than the cost of manufacturing an assembly having thesame capacity composed of separate units with interconnecting externalducts. The structured configuration of the integrated assembly greatlysimplifies its erection at an operating site.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects andfeatures thereof, reference is made to the attached drawings wherein:

FIG. 1 schematically illustrates one embodiment of a two-stage heat pumpassembly in accordance with the invention.

FIG. 2 is a perspective view of the crown arrangement of opposingdiffuser ducts and impellers in the two-stage compressor, and

FIG. 3 schematically illustrates a second embodiment of the heat pumpassembly having three stages.

DESCRIPTION OF THE INVENTION

In accordance with a first embodiment of the present invention, a heatpump and a two-sage compressor are shown in FIG. 1. The heat pump is anintegrated heat pump assembly based on an gasdynamic arrangement inaccordance with the invention, all components of the assembly, exceptfor the motor 10, being contained within a cylindrical vessel 11.

The vessel is divided by partition walls 12 and 13 into an evaporatorchamber A, a condenser chamber B and a compressor chamber C. Theevaporator chamber A is equipped with headers 15 adapted to spreadentrant water or other coolant in thin “curtains” with a large surfacearea to promote its evaporation under partial vacuum conditions.

Evaporator chamber A opens into an intake duct 16 leading into theintake port of the compressor. The inlet of intake duct 16 is covered bya mist eliminator 19 preventing the entrance of water droplets. Intakeduct 16 is coaxial with the cylindrical vessel 11, and, together withpartitions 12 and 13, defines the annular condenser chamber B. In thecondenser chamber B, there is a plurality of nozzles 22 mounted on thecylindrical wall of the vessel 11 and adapted to spray cooling waterinto the chamber.

Compressor chamber C houses the first and second stages of a centrifugalcompressor, both coaxial with vessel 11. Chamber C is subdivided intotwo cells C1 and C2 by an intermediate partition wall 24 placed betweenthe two compressor stages. The first stage is provided with an impeller26 rotatable within a stationary shroud 27 and is adapted to dischargepartially compressed vapor through an array of diffuser ducts 28 throughpartition wall 24 and cell C2 toward the intake port of the secondcompressor stage impeller 29. The annular cell C2 is equipped with meansfor intercooling or de-superheating the vapor between the two compressorstages such as water spray nozzles 31. In the flow path to the intakeport of the second stage, there is provided a mist eliminator 33.

The second stage impeller 29 is rotatable within a stationary shroud 35and is adapted to discharge compressed vapor through an array ofdiffuser ducts 37 and apertures in partition wall 24 into the annularcell C1 of the compressor chamber C which opens into condenser chamber Bthrough a discharge port 38.

Impellers 26 and 29 of the first and second stages of the compressor aremounted on a common shaft 40 supported by a bearing house 42 disposedbetween them. Shaft 40 is coupled to the external motor 10 through agear box 43. Thus a single motor can concurrently drive both stages ofthe compressor.

As indicated by arrows, water vapor generated in evaporator chamber A isdrawn by a suction force produced by the compressor to the first stageintake via mist eliminator 19 and intake duct 16. The first stageimpeller 26 partially compresses the vapor and discharges it to secondstage intake via diffuser ducts 28 and cell C2, through mist eliminator33. In cell C2, partially compressed vapor is de-superheated by coolwater sprayed from nozzles 31 or by suitable heat exchange surfaces (notshown in FIG. 1).

The second stage impeller 29 completes vapor compression and sends thevapor to cell C1 of compressor chamber C via diffuser ducts 37. Next,vapor enters annular condenser chamber B and is condensed there by meansof cooling water sprayed from nozzles 22. The heated cooling waterleaves condenser chamber B through outlet 44. The chilled water ispumped through outlet 45.

The flow path of the vapor between compressor stages is organized in aunique gasdynamic arrangement shown in FIG. 2. The discharge of bothimpellers leaving the shroud in radial direction through the peripheraldischarge zone 46 is conveyed by a plurality of curved ducts 28 and 37.Ducts 28 form a crown-like array around the first impeller 26, each ductbending gradually towards partition wall 24 (not shown in FIG. 2) andending in an aperture P1 in said wall. Ducts 37 form a similar arrayaround the second impeller 29 and also end in apertures P2 on partitionwall 24 but from the opposite side. The apertures P1 and P2 are arrangedin an alternating pattern on partition wall 24 allowing the oppositevapor flows from the two impellers to bypass each other in a veryeffective way. Ducts 28 and 37 have a diffuser form, with thecross-section area gradually increasing from impeller periphery 46 topartition wall 24, whereby the vapor flow slows down and its pressureincreases.

Reverting to FIG. 1, the vapor stream indicated by arrows greatly slowsdown in diffuser ducts 37, passes through discharge port 38, and flowsinto condenser chamber B surrounding the intake duct 16. This gasdynamicarrangement saves space and, together with the above-mentioned mutualby-pass of the impeller discharge flows, allows a very compact andaerodynamically effective layout of the heat pump assembly. The layoutis also mechanically effective since the short twin-impeller shaft canbe supported by one bearing house and driven by a short shaft line. Thewhole heat pump assembly with the exception of the motor can thus beaccommodated in a simple cylindrical housing of approximately twice theimpellers' diameter.

This configuration substantially reduces the cost of manufacturing andinstalling the assembly, simplifying to a significant degree theerection and maintenance of the assembly at its site of service. It alsominimizes gas/vapor pressure losses, thereby improving the compressionratio and the efficiency of the assembly.

The assembly as a whole can be made even more compact by placing asuitably designed electric motor between the two impellers instead ofthe bearing house, the shaft line and the external motor.

Another embodiment of a heat pump assembly of the present invention isshown in FIG. 3 and demonstrates the manner in which a two-stagecompressor may be expanded to three stages and more. The arrangement isidentical to that shown in FIG. 1 except that it includes a thirdcompressor stage introduced next to intake duct 16. Impeller 48 of thethird stage is mounted on an extension 50 of drive shaft 40, whichextension is supported by a second bearing house 52 coaxial with thecylindrical vessel 11. Impeller 48 is rotatable in a shroud 53.

A second partition wall 54 is introduced, with apertures P1′ and P2′similar to apertures in partition wall 24. The peripheral discharge zoneof impeller 48 is connected to apertures P1′ on partition wall 54 by acrown-like array of diffuser ducts 57 similar to ducts 28. Ducts 37,from the peripheral discharge zone of second impeller 29 to apertures P2on partition wall 24, are extended to apertures P2′ on the secondpartition wall 54.

A new cell C3 is defined between partition walls 24 and 54 adapted toconvey compressed vapor from third stage impeller 48 via diffuser ducts57 to the intake port of first stage impeller 26. Intercooling sprayheads 61 may be accommodated in the new cell C3, in which case anintermediate partition wall 63 carrying mist eliminators 65 isintroduced in the flow path, and diffuser ducts 57 are extended tointermediate partition wall 63.

From gasdynamic point of view, impellers 48, 26, and 29 should now bedesignated first, second, and third stage impellers, respectively. Itcan be readily seen from the above that more stages may be introduced inexactly the same manner downstream of intake duct 16.

While there have been shown preferred embodiments of the invention, itis to be understood that many changes may be made therein withoutdeparting from the spirit of the invention. Thus, the assembly, insteadof containing within the cylindrical vessel a multi-stage centrifugalcompressor, may contain in concentric relation with the vessel a singlestage compressor.

1. Gasdynamic arrangement for a multi-stage centrifugal turbomachinehaving an intake duct (16) and a discharge port (38), and comprising: a)a first impeller (26) with axial intake port and radial peripheraldischarge zone, said axial intake port being in fluid communication withsaid intake duct; b) a second impeller (29) with axial intake port andradial peripheral discharge zone, said second impeller disposedcoaxially with said first impeller, the two impellers being located attwo sides of an imaginary plane crossing their common axis; c) a firstmeans for conducting the flow from the peripheral discharge zone of thefirst impeller to the intake port of the second impeller along a firstflow path (28, C2) including a plurality of first curved ducts (28) inaxisymmetric arrangement; d) a second means for conducting the flow fromthe peripheral discharge zone of the second impeller towards saiddischarge port of the machine along a second flow path (37, C1)including a plurality of second curved ducts (37) in axisymmetricarrangement; wherein said first and said second flow paths (28, 37)leave the respective peripheral discharge zones bending graduallytowards said imaginary plane, said first and said second flow pathscross said imaginary plane in opposite directions and, after crossingsaid imaginary plane, the two flow paths lie entirely at different sidesof the imaginary plane, and wherein said first and said second curvedducts (28, 37) have diffuser shape with cross-section area increasingfrom the impeller periphery discharge zone to said imaginary plane. 2.Gasdynamic arrangement according to claim 1, comprising a partition wall(24) between said impellers (26, 29), said wall lying substantially insaid imaginary plane and having a plurality of first apertures (P1) anda plurality of second apertures (P2), wherein: a) said plurality offirst curved ducts (28) connects the peripheral discharge zone of thefirst impeller (26) to said plurality of first apertures P1, and saidfirst means for conducting the flow further comprises a first outershell (C1) defining, together with said partition wall (24), a chamberconducting the flow from said plurality of first apertures P1 to theintake of the second impeller (29), said chamber at least partiallyencompassing said second impeller; b) said plurality of second curvedducts (37) connects the peripheral discharge zone of the second impeller(29) to said plurality of second apertures (P2), and said second meansfor conducting the flow further comprises a second outer shell (C2)defining, together with said partition wall (24), a chamber conductingthe flow from said plurality of second apertures (P2) towards saiddischarge port (38).
 3. Gasdynamic arrangement according to claim 2,wherein: a) said plurality of first curved ducts (28) are arranged in afirst crown array around the first impeller (26); b) said plurality ofsecond curved ducts (37) are arranged in a second crown array around thesecond impeller (29); c) said plurality of first apertures (P1) on thepartition wall (24) connected to the plurality of first curved ducts(28) are positioned in alternating pattern between said plurality ofsecond apertures (P2) connected to the plurality of second curved ducts(37).
 4. Gasdynamic arrangement according to claim 2, wherein saidturbomachine is encased in a substantially integral axisymmetric shell(C) coaxial with said impellers (26, 29), said first and second outershells (C1, C2) being part of said integral shell.
 5. Gasdynamicarrangement according to claim 4, wherein said discharge port (38) ofthe turbomachine is located substantially at the same side of saidintegral shell (C) as the inlet of said intake duct (16).
 6. Gasdynamicarrangement according to claim 4, wherein said integral axisymmetricshell (C) is formed as a cylinder with diameter approximately twice thediameter of the impellers.
 7. Gasdynamic arrangement for a multi-stagecentrifugal turbomachine according to claim 2, wherein said fluidcommunication between the intake port of the first impeller (26) and theintake duct (16) is performed via at least one additional stage in thefollowing way: a) an additional impeller (48) having an axial intakeport and a radial peripheral discharge zone is disposed coaxiallybetween said intake duct and said intake port of the first impeller, theintake port of the additional impeller being at the side of andconnected to the intake duct (16); b) an additional partition wall (54)with a plurality of first apertures (P1′) and a plurality of secondapertures (P2′) is situated between the additional impeller (48) and theintake port of the first impeller in a plane perpendicular to the axisof the impellers; c) an additional plurality of curved ducts (57) isadded to connect the peripheral discharge zone of the additionalimpeller to said plurality of first apertures (P1′) on the additionalpartition wall (54); d) said plurality of second curved ducts (37)connecting the peripheral discharge zone of the second impeller (29) tothe plurality of second apertures (P2) in the existing partition wall(24) is extended to the plurality of second apertures (P2′) in theadditional partition wall (54).
 8. A multi-stage centrifugal compressorhaving the gasdynamic arrangement for multi-stage turbomachine accordingto claim
 1. 9. A two-stage centrifugal compressor according to claim 8,wherein said first and second impeller are mounted on a common impellershaft (40) adapted to be driven by one motor (10).
 10. A two-stagecentrifugal compressor according to claim 9, wherein said impeller shaft(40) is supported by one bearing house (42) disposed between said firstand second impellers.
 11. A two-stage centrifugal compressor accordingto claim 9, wherein said common impeller shaft is the shaft of saidmotor, said impellers being mounted on the two ends of said shaft.
 12. Aheat pump comprising a two-stage centrifugal compressor according toclaim 8 with an intake duct (16), a discharge port (38), and a drivingmotor (10), the heat pump further comprising an evaporation chamber (A),in fluid connection with said intake duct, and a condenser chamber (B),in fluid connection with said discharge port, and an integralaxisymmetric housing (11) coaxial with the compressor, accommodating allelements of said pump or all elements except for the driving motor. 13.A heat pump according to claim 12, wherein said integral housing (11) isdivided into chambers by transverse separation walls (12, 13), saidchambers being arranged in the following order along the axis of thehousing: a) evaporator chamber (A), b) condenser chamber (B) surroundingsaid intake duct (16), c) compressor chamber (C), the evaporator chamber(A) being opened towards the intake duct (16), the discharge port (38)of said two-stage compressor being opened towards said condenser chamber(B).
 14. A heat pump according to claim 13, wherein said heat pumpcomprises further: means (15) to feed water into said evaporatorchamber; means (22) to spray water into said condenser chamber; means(45) to pump out chilled water; means (44) to pump out heated coolingwater; and at least one of the following devices: means (33) for mistelimination situated prior to flow entry into impeller intake ports;means (31) for intercooling the compressed gas situated in the flow pathbetween said impellers.
 15. A heat pump according to claim 12, whereinsaid condenser chamber (B) is arranged as an annular chamber around saidintake duct (16), said discharge port (38) opening into said condenserchamber.